diff-index Git Command Guide

The git diff-index command is used to compare the content and mode of the blobs found in a tree object with the corresponding tracked files in the working tree, or with the corresponding paths in the index. When path arguments are present, it compares only paths matching those patterns. Otherwise, all tracked files are compared.

git diff-index Syntax:

git diff-index [-m] [--cached] [--merge-base] [<common-diff-options>] <tree-ish> [<path>...]

Options:

Option	Description
-m	Consider merge commits when comparing
—cached	Compare the index instead of the working tree
—merge-base	Compare with the merge-base of the given commits
-p, —patch	Generate patch (combined with other options)
-s, —no-patch	Suppress diff output
—stat	Show diffstat
-U, —unified=	Generate diffs with lines of context
—raw	Generate the diff in raw format (default)
—color	Show colored diff

Parameters:

Parameter	Description
	The tree object to compare (e.g., HEAD, commit hash)
…	Optional paths to limit the comparison to specific files or directories

Caution

Note that —cached mode compares the index contents with the given tree, while the default behavior compares the working tree with the index. Ensure the tree-ish refers to a valid commit or tree object.

git diff-index Command Samples:

Compare working tree with HEAD

git diff-index HEAD

Shows differences between the current working tree and the HEAD commit.

Compare index with HEAD (staged changes)

git diff-index --cached HEAD

Shows what would be committed if you ran git commit.

Compare specific file

git diff-index HEAD -- myfile.txt

Compares only the specified file with the HEAD commit.

Generate patch format output

git diff-index -p HEAD

Generates patch information showing context and differences.

Show abbreviated output

git diff-index --abbrev HEAD

Shows differences with abbreviated SHA-1 hashes.

Use cached mode without patch

git diff-index --cached --no-patch HEAD

Shows raw differences in the index vs HEAD without patch details.

Tip

Use git diff-index —cached HEAD to preview exactly what will be committed, equivalent to git write-tree vs HEAD comparison.

How do I see what files have changed in the working tree compared to HEAD?

To see what files have changed in the working tree compared to HEAD, use:

git diff-index HEAD

How do I compare staged changes to HEAD?

To compare what is in your index (staged changes) to HEAD, execute:

git diff-index --cached HEAD

How can I use git diff-index to compare only specific files?

To compare only specific files with the tree, use the path arguments:

git diff-index HEAD -- file1.txt file2.txt

What is the difference between —cached and non-cached modes in git diff-index?

—cached mode compares the index contents with the specified tree, while the default mode compares the working tree with the index. Use —cached to see what will be in your next commit.

How do I generate patch output with git diff-index?

To generate patch format output showing changes, use:

git diff-index -p HEAD

How can I suppress the content and just show which files changed?

To show only file names and status without showing the actual differences, use:

git diff-index --name-only HEAD

Applications of the git diff-index command

1. Previewing exactly what changes will be included in the next commit
2. Comparing working tree state against any commit or tree in history
3. Scripting automated repository checks and validation
4. Detecting file renames, permission changes, and exact differences
5. Building custom Git workflows and integrations requiring low-level diff operations